The constellation Orion

The constellation Orion

Today I would like to talk about my favorite constellation, the constellation of Orion.

It dominates the winter sky and is easily recognizable, especially the belt formed by the stars Mintaka, Alnilam and Alnitak. The constellation is very close to the celestial equator, and this allows almost all the peoples of the Earth to observe it.

Historically, Orion has always aroused great admiration for men. The Sumerians, for example, saw the depiction of a sheep. For the ancient Egyptians, however, Orion was the celestial representation of Osiris and, according to some historians, the three pyramids of Giza would be oriented just like the stars of the belt. For the Chinese, this constellation was one of 28 zodical Xiu. According to a myth of Greek origin, Orion was the son of Poseidon and Eurialus, daughter of King Minos of Crete. Homer describes him as a powerful hunter, armed with a bronze staff. Tradition tell us that the hunter Orion, in the sky is followed by his dogs (the two constellations Canis Major and Canis Minor). Another myth instead sees Orion fighting with a large bull, and in fact Orion is very close to the Taurus. There are also several legends about the death of Orion, but many agree that the hunter would be fatally stung by a scorpion. Precisely for this reason, the two constellations Orion and Scorpio are at the extremes of the sky, at the greatest distance possible, as if he were still terrorized by the animal that had killed him.

The constellation Orion

The three stars of the Orion belt: Mintaka, Alnilam, Alnitak.

This constellation is located right on the Milky Way and is full of stars and wonderful objects.

The main stars are:

  • Rigel (β Orionis), a blue supergiant with three small companion stars
  • Salpha (κ Orionis), a blue star of magnitude 2.0
  • Bellatrix (γ Orionis), a blue giant of magnitude 1,7
  • Betelgeuse (α Orionis), a record-breaking red supergiant, in fact if it were in our solar system it could encompass all the planets up to Jupiter!
  • Mintaka, Alnilam, Alnitak (δ Orionis, ε Orionis, ζ Orionis), the three stars that together form the famous belt of Orion

The constellation Orion

The Orion Nebula (M42)

Orion is also rich in non-stellar objects, above all nebulae.

To the south of the belt, already with the naked eye, it is possible to see the famous Orion Nebula, listed as M42 in the famous catalog of Charles Messier. This nebula is a great classic for astrophotography, already appears in all its glory after a few seconds of exposure and is also visible with a simple pair of binoculars. The nebula is mainly formed by hydrogen ionized by the young and warm stars that are inside it.

In the vicinity of Alnitak we find two other great classics, more elusive than the Orion Nebula: the Flame Nebula and the Horsehead Nebula. The latter, in particular, is formed by dark powders that stand out against the background of ionized gas, especially hydrogen, from the nearby star Alnitak. It is estimated that this nebula has a mass of 27 solar masses, and is destined to disintegrate completely over the next 5 million years.

All around the constellation, finally, there is a diffuse nebulosity that takes the name of Barnard Ring. The latter is part of an immense region of molecular gas, which also includes the Orion Nebula and the Horsehead Nebula. It is estimated that this gas region has a diameter of about 300 light years and that it is formed by the explosion of a supernova occurred about 2 million years ago.

Orion is also rich in stars and star clusters, among which we remember the extremities of the hunter’s sword, ie the star clusters NGC 1980 and NGC 1981.

This constellation is very special to me, as everything started here. I had unconsciously observed it as a child and was also the starting point to orient myself in the sky.

 

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